Recently, a photoelectric conversion device, which is a power generation means that generates power without carbon dioxide emissions, has attracted attention as a countermeasure against global warming. A solar cell for supplying residential power or the like, which generates power from sunlight outdoors, is known as a typical example thereof. For such a solar cell, a crystalline silicon solar cell using single crystal silicon or polycrystalline silicon is mainly used.
An uneven structure is provided on a surface of a solar cell using a single crystal silicon substrate or a polycrystalline silicon substrate in order to reduce surface reflection. The uneven structure provided on the surface of the silicon substrate is formed by etching the silicon substrate with an alkaline solution such as an aqueous sodium hydroxide solution. Since the etching rate by the alkaline solution varies depending on a crystal plane orientation of silicon, when a silicon substrate with a (100) plane is used for example, a pyramidal uneven structure is formed.
Although the above uneven structure can reduce surface reflection of the solar cell, the alkaline solution used for etching causes contamination of the silicon substrate. In addition, since etching characteristics considerably vary depending on the concentration or temperature of the alkaline solution, it is difficult to form the uneven structure on the surface of the silicon substrate with high reproducibility. For the difficulty, a combination method of a laser processing technique and chemical etching is disclosed (for example, see Patent Document 1).
On the other hand, in a solar cell whose photoelectric conversion layer is formed using a semiconductor thin film of silicon or the like, it is difficult to form an uneven structure on a surface of the silicon thin film by above etching using an alkaline solution.